Generally, electronic field devices (such as process transmitters) are used to monitor the operation of industrial processes such as those in oil refineries, chemical processing plants, paper processing plants, biotechnology plants, pharmaceutical plants, food and beverage plants, and the like. Process transmitters for monitoring an industrial process may measure pressure, flow rate, fluid or material level in a tank, temperature, vibration, and the like. Additionally, such field devices may include analytical electronics, diagnostic electronics, or other process monitoring electronic devices, or even electronic, hydraulic or pneumatic actuator devices used for industrial process control.
Process transmitters are typically positioned within the processing plant in locations where liquids, dust and humidity and various industrial contaminants may be present. In some environments, process liquids such as acid solutions or base solutions can be present. Liquids may also include spray from hoses used to clean plant equipment. Liquids can drip, splash or spray onto the process transmitter and its electrical connections. Additionally, dust, humidity, and liquids in the environment may contaminate and degrade the electrical connections to and within the process transmitter.
Transmitters that include circuitry disposed in a sealed housing and protected by an outer cover are known in the art. It is also known to include one or more actuatable switches for modifying a parameter of the circuit, such as a zero or span setting. Typically, the one or more switches or the field wiring terminals are accessible only after removal of the outer transmitter cover.
Unfortunately, removal of the outer cover exposes the electronics within the transmitter housing to contaminants and electromagnetic and radio frequency interference. One technique for maintaining EMI protection for electronics within the transmitter housing includes an electrically conductive inner cover disposed within the transmitter housing and in frictional contact with electrically conductive walls of the housing to reduce the effects of EMI when the outer cover is removed. One example of a process transmitter with an inner conductive cover is shown and described in U.S. Pat. No. 5,353,200 issued to Bodin et al. and entitled “PROCESS TRANSMITTER WITH INNER CONDUCTIVE COVER FOR EMI SHIELDING” issued Oct. 4, 1994, which is incorporated herein by reference in its entirety.
There is an ongoing need in the art for industrial process transmitter housing configurations with improved humidity and environmental contamination robustness as well as efficient EMI/RFI filtering capabilities. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.